Method for manufacturing ring-shaped glass spacer

ABSTRACT

A method for manufacturing the ring-shaped glass spacer to be arranged in contact with a magnetic disk in a hard disk drive apparatus, including: preparing a ring-shaped glass blank; and grinding main surfaces of the ring-shaped glass blank by using grinding pads that include diamond particles as fixed abrasive particles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.17/006,733, filed on Aug. 28, 2020, which is a continuation applicationof U.S. patent application Ser. No. 16/634,128, filed on Jan. 24, 2020,which is U.S. National stage application of International PatentApplication No. PCT/JP2018/036747, filed on Oct. 1, 2018, which, inturn, claims priority to Japanese Patent Application No. 2017-191256,filed in Japan on Sep. 29, 2017, the entire contents of which are herebyincorporated herein by reference.

BACKGROUND Field of the Invention

The present invention relates to a ring-shaped glass spacer to bearranged in contact with a magnetic disk in a magnetic recording harddisk drive apparatus, and a hard disk drive apparatus in which the glassspacer is used.

Background Information

Following the expansion of cloud computing in recent years, many harddisk drive apparatuses (hereinafter referred to as HDD apparatuses) areused in a data center for a cloud in order to increase the storagecapacity. Thus, there are demands for increasing the storage capacity ofHDD apparatuses, as compared with that achieved by conventionaltechniques.

In conventional HDD apparatuses, the recording density has beenincreased by reducing the float distance between a magnetic head and amagnetic disk and reducing the size of magnetic particles that areprovided on magnetic disks, but these measures will reach their physicallimits in coming years, and therefore the above-described demands forincreasing the storage capacity of HDD apparatuses are not sufficientlysatisfied. Therefore, consideration can be given to increasing thenumber of magnetic disks that are installed in an HDD apparatus.

Incidentally, ring-shaped spacers for magnetic disks are providedbetween magnetic disks installed in an HDD apparatus in order to keepthe magnetic disks in a state of being spaced apart from each other.These spacers function to keep the magnetic disks from coming intocontact with each other and precisely arrange the magnetic disks atpredetermined positions spaced apart from each other. On the other hand,the spacers are in contact with the magnetic disks, and accordingly, ifthe spacers rub against the magnetic disks due to relative displacementbetween the spacers and the magnetic disks, for example, foreign matter,such as minute particles, may be generated by the spacers. In this case,long-term reliability of the HDD apparatus is likely to be impaired bythe generated minute particles. Therefore, it is desirable to mitigateminute particles generated by the spacers.

As such a spacer, a glass spacer is known that has an average surfaceroughness of 0.001 to 0.005 μm in a portion (a main surface of thespacer) that comes into contact with a substrate (Japanese Patent No.4136268).

The surface roughness of the main surfaces of the above-described spaceris small, and therefore generation of minute particles can besuppressed. However, if the surface roughness of main surfaces of aspacer is reduced, an adhesive force that acts between the spacer and amagnetic disk is increased and the following problem may occur.

Glass spacers and magnetic disks are installed in an HDD apparatus byalternately stacking the magnetic disks and the spacers with a spindleof the HDD apparatus passing through inner holes of the magnetic disksand the spacers, and then pressing the magnetic disks and the spacers inan axial direction of the spindle.

An inspection such as a performance test is performed on HDD apparatusesafter installation. If a problem is found in an HDD apparatus in aperformance test or the like, the stacked magnetic disks and spacers aresequentially removed from the spindle to remove a faulty magnetic disk.At this time, a spacer and a magnetic disk may be adhered to each otherand unseparable from each other, because the spacers and the magneticdisks are strongly pressed in the axial direction of the spindle to comeinto contact with each other. Therefore, it is preferable to reduce anadhesive force between a magnetic disk and a spacer as much as possible.

In particular, if a large number of magnetic disks are installed in anHDD apparatus, a large number of spacers are also provided between themagnetic disks, and accordingly the possibility of adhesion occurringbetween the magnetic disks and the spacers further increases.

In recent years, the above-described problem of adhesion has become moresevere, because the surface roughness of main surfaces of magnetic diskshas been further reduced to increase the recording density.

SUMMARY

Therefore, an object of the present invention is to provide a glassspacer that can suppress the occurrence of adhesion between a magneticdisk and a spacer when magnetic disks and spacers are removed from anHDD apparatus in which the magnetic disks and the spacers are installed.

One aspect of the present invention is a method for manufacturing thering-shaped glass spacer to be arranged in contact with a magnetic diskin a hard disk drive apparatus, including: preparing a ring-shaped glassblank; and grinding main surfaces of the ring-shaped glass blank byusing grinding pads that include diamond particles as fixed abrasiveparticles.

According to the above-described glass spacer, the occurrence ofadhesion between a magnetic disk and a spacer can be suppressed whenmagnetic disks and spacers are removed from the HDD apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external perspective view of a spacer for magnetic disksaccording to one embodiment.

FIG. 2 is a diagram showing an arrangement of spacers according to oneembodiment and magnetic disks.

FIG. 3 is a cross-sectional view showing a main portion of an exemplarystructure of an HDD apparatus in which spacers according to oneembodiment are installed.

FIG. 4A is a diagram schematically showing one example of an unevenshape of main surfaces of a spacer according to one embodiment, and FIG.4B is a diagram schematically showing one example of an uneven shape ofmain surfaces of a conventional spacer.

DESCRIPTION OF EMBODIMENTS

The following describes a glass spacer of the present invention indetail.

FIG. 1 is an external perspective view of a glass spacer (hereinaftersimply referred to as a spacer) 1 according to one embodiment, and FIG.2 is a diagram showing an arrangement of spacers 1 and magnetic disks 5.FIG. 3 is a cross-sectional view showing a main portion of an exemplarystructure of an HDD apparatus in which the spacers 1 are installed.

The spacers 1 are installed in an HDD apparatus by alternately stackingthe magnetic disks 5 and the spacers 1 on each other as shown in FIG. 2.As shown in FIG. 3, the plurality of magnetic disks 5 are fitted to aspindle 14 that is connected to a motor 12 and rotates, such that thespindle 14 passes through the magnetic disks 5 and the spacers 1 areinterposed between the magnetic disks 5, and the magnetic disks 5 arefixed to the spindle 14 by being pressed from above using a screw via atop clamp 16 that is located above the magnetic disks 5, and thus themagnetic disks 5 are attached at predetermined intervals.

As shown in FIG. 2, the spacers 1 and the magnetic disks 5 arealternately arranged such that one spacer 1 is located between twomagnetic disks 5, and the spacers 1 keep a gap between adjacent magneticdisks 5 at a predetermined distance. It should be noted that, althoughthe spacer 1 described in the following embodiment is provided betweentwo magnetic disks 5 while being in contact therewith, the presentinvention also applies to a spacer that is in contact with only theuppermost or lowermost magnetic disk 5.

As shown in FIG. 1, the spacer 1 has a ring shape and includes an outercircumferential edge surface 2, an inner circumferential edge surface 3,and main surfaces 4 that are opposite to each other. A chamfered surface(not shown) may be provided in a surface of the spacer 1, asappropriate.

The inner circumferential edge surface 3 is a surface that comes intocontact with the spindle 14, and is a wall surface that surrounds a holethat has an inner diameter that is slightly larger than the outerdiameter of the spindle 14.

The main surfaces 4 are two surfaces that are parallel to each other andcome into contact with the magnetic disks 5. The spacer 1 fixes themagnetic disks 5 using a frictional force while being in contact withmain surfaces of the magnetic disks 5.

Therefore, the surface roughness Ra (arithmetic average roughness) andthe average inclination RΔa of the main surfaces 4 that come intocontact with the magnetic disks 5 are determined as described below.

Here, Ra (arithmetic average roughness) and Rz (maximum height), whichwill be described as surface roughness parameters, conform to JIS B0601-2001 (ISO 4287-1997). Also, the average inclination RΔa conforms toASME B46-1995. These parameters are calculated by, for example, usingdata that is measured using a stylus surface roughness measurementdevice in which a stylus is used. For example, a stylus in which theradius of curvature of a leading end is 2 μm and the taper angle of acone is 60° is used. Other measurement/calculation parameters are set asfollows, for example: a measurement length of 400 μm, a measurementresolution (pitch: ΔX) of 0.1 μm, a scan speed of 0.1 mm/sec, a lowpassfilter cut-off value (Ls) of 2.5 μm, and a highpass filter cut-off value(Lc) of 80 μm.

Specifically, the surface roughness Ra of the main surfaces 4 of thespacer 1, which come into contact with the magnetic disks 5, is notlarger than 1.0 μm. The spacer 1 is made of glass that is a fragilematerial, and therefore, if the above-described surface roughness Ra islarger than 1.0 μm, when the spacer 1 comes into contact with a magneticdisk 5, foreign matter, such as minute particles, is generated by thespacer 1 as a result of tips of protrusions that constitute surfaceirregularities of the main surfaces 4 being broken, for example, and asa result, long-term reliability of the HDD apparatus is impaired.Therefore, the above-described surface roughness Ra is not larger than1.0 μm. Further, the average inclination RΔa of the main surfaces 4 thatis obtained using the following Equation (1) is at least 0.02.

$\begin{matrix}{{R\Delta a} = {\frac{1}{n}{\sum\limits_{i = 1}^{n}{\frac{dz_{i}}{dX}}}}} & (1)\end{matrix}$

Here, dz_(i)/dX is expressed by the following Equation (2), ΔXrepresents a data interval [μm] between measurement data pieces ofsurface roughness, which corresponds to the measurement resolution(pitch) of 0.1 μm in the above example, z_(i) (i is a natural number)represents the i-th measurement data piece. n represents a total number(n>6) of measurement data pieces.

$\begin{matrix}{\frac{dz_{i}}{dX} = {\frac{1}{{60 \cdot \Delta}\; X}( {z_{i + 3} - {9z_{i + 2}} + {45z_{i + 1}} - {45z_{i - 1}} + {9z_{i - 2}} - z_{i - 3}} )}} & (2)\end{matrix}$

Equation (2) is an equation that is used in a Savitzky-Golay filter. Itshould be noted that, if i in dz_(i)/dX is 1, 2, 3, (n−2), (n−1), or n,z⁻², z⁻¹, z₀, Z_(n+1), Z_(n+2), and z_(n+3) appear on the right-handside of Equation (2), but these are not included in the total number ofn measurement data pieces. In this case, auxiliary measurement datapieces that correspond to z⁻², z⁻¹, z₀, Z_(n+1), Z_(n+2), and z_(n+3)are used from auxiliary measurement data pieces that have been measuredfor an auxiliary purpose in ranges that are adjacent to the measurementrange, before or after measurement is performed to obtain the nmeasurement data pieces.

If the surface roughness Ra is set to be not larger than 1.0 μm asdescribed above, the spacer 1 has small irregularities, and accordinglythe number of generated minute particles is reduced. Also, it can beexpected that the surfaces of the magnetic disks 5 are unlikely to bedamaged by the irregularities formed in the main surfaces 4 of thespacer 1. From the same standpoint, the surface roughness Ra ispreferably not larger than 0.7 μm, and more preferably not larger than0.5 μm.

On the other hand, as the surface roughness Ra of the main surfaces 4 ofthe spacer 1 is reduced, an adhesive force between the spacer 1 and themagnetic disks 5 increases. If the adhesive force is too strong, it maybe difficult to separate the spacer 1 and the magnetic disks 5, whichadhere to each other, from each other when removing the magnetic disks 5and the spacer 1 from the HDD apparatus.

As described above, an inspection such as a performance test isperformed on HDD apparatuses after installation. If a problem is foundin an HDD apparatus in a performance test or the like, the stackedmagnetic disks 5 and spacers 1 are sequentially removed from the spindle14 to remove a faulty magnetic disk 5. At this time, if a magnetic disk5 and a spacer 1 are adhered to each other, the spacer 1 may beunseparable from the magnetic disk 5, or foreign matter may be generatedwhen the spacer 1 is separated and minute particles of the foreignmatter may attach to the surface of the magnetic disk 5. Such minuteparticles impair long-term reliability of the HDD apparatus.

Therefore, in order to suppress adhesion between the magnetic disk 5 andthe spacer 1, the average inclination RΔa is set to be at least 0.02 inthe present embodiment while the surface roughness Ra is set to be notlarger than 1.0 μm. From the same standpoint, the average inclinationRΔa is preferably at least 0.05, and more preferably at least 0.10.Although it is not always necessary to set the upper limit of theaverage inclination RΔa, the upper limit may be set to 0.3, for example.If the average inclination RΔa is larger than 0.3, there is a risk thatthe surface of the magnetic disk 5 will be damaged.

If the magnetic disk 5 and the spacer 1 adhere to each other, themagnetic disk 5 and the spacer 1 are separated from each other using astrong force, and therefore a portion of the surface of the magneticdisk 5 may be detached as minute particles. Such minute particles arenot preferable because they cause impairment of long-term reliability ofthe HDD apparatus when attached to magnetic disks. If the surfaceroughness Ra is not larger than 1.0 μm and the average inclination RΔais at least 0.02, adhesion between the magnetic disk 5 and the spacer 1can be suppressed, and accordingly the number of generated minuteparticles can also be reduced.

Even if the surface roughness Ra of the main surfaces 4 is the same, thesurfaces can have various uneven shapes. FIG. 4A is a diagramschematically showing one example of an uneven shape of the mainsurfaces of the spacer according to one embodiment, and FIG. 4B is adiagram schematically showing one example of an uneven shape of mainsurfaces of a conventional spacer. Even if the surface roughness Ra isthe same, the average inclination RΔa is different between a case inwhich the cycle of protrusions and depressions is short and a case whichthe cycle of protrusions and depressions is long, as shown in FIGS. 4Aand 4B. The average inclination RΔa of an uneven shape in which thecycle of protrusions and depressions is short is larger than the averageinclination RΔa of an uneven shape in which the cycle of protrusions anddepressions is long. The main surfaces 4 have protrusions anddepressions that have a short cycle, and therefore the magnetic disk 5and the spacer 1 are unlikely to adhere to each other.

It should be noted that, in the above-described Equation (2) fordefining the average inclination RΔa, ΔX is preferably 0.05 to 0.2 μm,preferably 0.08 to 0.12 μm, and particularly preferably 0.1 μm. It ispreferable that ΔX is in the above-described range and the averageinclination RΔa is at least 0.02.

According to one embodiment, it is preferable that the surface roughnessRa of the spacer 1 is at least 0.01 μm. If the surface roughness Ra issmaller than 0.01 μm, the magnetic disk 5 is unlikely to be damaged, butthere is a risk that, when the spindle 14 is rotated, surfaces of themagnetic disk 5 and the spacer 1 that are in contact with each otherwill slide against each other and be displaced relative to each other.This is due to the influence of a lubricant that is provided on thesurface of the magnetic disk 5. The lubricant is a liquid, and thereforemoves to fill a space between the surfaces in contact with each other,and has a function of facilitating sliding in a direction that isparallel to the main surfaces of the spacer 1 or the magnetic disk 5 andincreasing the adhesive force in a direction in which the magnetic disk5 and the spacer 1 are separated from each other (i.e., a directionperpendicular to the main surfaces 4). In particular, a film of thelubricant with a thickness of about 1 nm is normally formed on thesurface of the magnetic disk 5, and if this lubricant film is attachedto the surface of the spacer 1 and fills portions of grooves thatconstitute the uneven shape of the main surface 4 of the spacer 1, thereis a risk that the spacer 1 or the magnetic disk 5 will be more likelyto slide against the other in the direction parallel to the mainsurfaces of the spacer 1 or the magnetic disk 5, and the adhesive forcebetween the spacer 1 and the magnetic disk 5 will be further increasedin the direction perpendicular to the main surfaces 4. This phenomenonis considered as being caused by the influence of a meniscus force ofthe lubricant, and is more likely to occur if the thickness of thelubricant film is increased.

In view of the above, the adhesive force between the magnetic disk 5 andthe spacer 1 can be reduced by setting the surface roughness Ra to be atleast 0.01 μm and not larger than 1.0 μm and setting the averageinclination RΔa to be at least 0.02. In order to more reliably reducethe adhesive force between the magnetic disk 5 and the spacer 1, thesurface roughness Ra is preferably at least 0.05 μm, more preferably atleast 0.1 μm, and yet more preferably at least 0.3 μm.

According to one embodiment, it is preferable that a metal film isformed at least on the main surfaces 4 of the spacer 1 that come intocontact with the magnetic disks 5. Specifically, the spacer 1, which ismade of glass, is an insulator, and therefore static electricity islikely to accumulate in the magnetic disks 5 and the spacer 1. This isnot preferable because, if the magnetic disks 5 and the spacer 1 arecharged, foreign matter or minute particles are likely to be adsorbed,and a recording element or a reproducing element of a magnetic head maybreak as a result of the accumulated static electricity being dischargedto the magnetic head. Therefore, it is preferable to form a metal film,which is a conductive film, on the surface of the spacer 1 to make thespacer 1 electrically conductive, in order to eliminate staticelectricity. The metal film is formed using an immersion method that isused for plating, such as electroless plating, a vapor-depositionmethod, a sputtering method, or the like. The metal film may containchromium, titanium, tantalum, tungsten, an alloy that contains any ofthese metals, or a nickel alloy, such as nickel phosphorus (NiP) ornickel tungsten (NiW), for example. It is preferable that the nickelalloy is nonmagnetic.

According to one embodiment, it is also preferable that theabove-described metal film is also formed on the outer circumferentialedge surface 2 and the inner circumferential edge surface 3, in additionto the main surfaces 4. If the metal film is formed on each of the upperand lower main surfaces 4 of the spacer 1, which come into contact withthe magnetic disks 5, it is sufficient to form the metal film on atleast one of the outer circumferential edge surface 2 and the innercircumferential edge surface 3 in order to electrically connect themetal films formed on the upper and lower main surfaces 4 to each other,and a configuration is possible in which the metal film is formed onlyon the inner circumferential edge surface 3, for example. In this case,electrical conductivity is further increased, and the ability toeliminate static electricity is increased. For the above-describedreason, it is most preferable to form the metal film on all surfaces ofthe spacer 1. The thickness of the metal film is only required to bethick enough to achieve electrical conductivity with which theabove-described static electricity can be released to the outside, andis 0.01 to 10 μm, for example. Even if such a metal film is formed onthe main surfaces 4, the numerical ranges of the surface roughness Raand the average inclination RΔa of the main surfaces 4 are theabove-described ranges.

It should be noted that, if the spacer 1 is made of conductive glass,static electricity can be released from the magnetic disks 5 to theoutside directly via the spacer 1, and therefore a configuration is alsopossible in which the metal film is not provided.

The above-described spacer 1 is preferably used in an HDD apparatus inwhich eight or more magnetic disks 5 are installed. If eight or moremagnetic disks 5, which is more than six magnetic disks 5 that arenormally installed in an HDD apparatus, are installed in an HDDapparatus, the magnetic disks 5 and the spacers 1 need to be morestrongly pressed (clamped) against each other using the top clamp 16,and therefore the pressure applied by the top clamp 16 needs to beincreased. As a result, the adhesive force between the spacers 1 and themagnetic disks 5 installed in the HDD apparatus is increased, andremoval failures are likely to increase when separating the spacers 1from the magnetic disks 5. However, as a result of the surface roughnessRa and the average inclination RΔa of the spacers 1 being limited to theabove-described numerical ranges, even if the pressure is increased, thespacers 1 and the magnetic disks 5 are unlikely to adhere to each otherand can be easily separated from each other. Spacers 1 that can suppressthe occurrence of removal failures as described above are preferable.For the same reason, the spacer 1 of this embodiment is more preferablyused in an HDD apparatus in which nine or more magnetic disks 5 areinstalled, and further preferably used in an HDD apparatus in which tenor more magnetic disks 5 are installed.

It is preferable that the magnetic disk 5 is obtained by forming amagnetic film on an aluminum alloy substrate or a glass substrate. Ifthe surface roughness Ra of the magnetic disk 5 is not larger than 0.3nm, the magnetic disk 5 is likely to adhere to the spacer 1, and if thesurface roughness Ra of the magnetic disk 5 is not larger than 0.2 nm,adhesion between the magnetic disk 5 and the spacer 1 is particularlylikely to occur. However, the spacer 1 of this embodiment has anexcellent effect of suppressing adhesion, and therefore adhesion can befavorably suppressed even if the surface roughness of the magnetic disk5 is in any of the above ranges. That is, the spacer 1 is preferablyused together with a magnetic disk 5 that has a surface roughness Ra ofnot larger than 0.3 nm, and particularly preferably used together with amagnetic disk 5 that has a surface roughness Ra of not larger than 0.2nm.

According to one embodiment, it is preferable that the surface roughnessRz (maximum height) of the outer circumferential edge surface 2 of thespacer 1 is 1.5 to 20 μm. In a case in which the spacer 1 is removed bygripping the outer circumferential edge surface 2 of the spacer 1 in areworking operation for removing a faulty magnetic disk from the HDDapparatus after installation, if the surface roughness Rz (maximumheight) is smaller than 1.5 μm, the spacer 1 may slip out of a grippingjig that grips the outer circumferential edge surface 2 of the spacer 1.If the surface roughness Rz (maximum height) is larger than 20 μm, asurface of the gripping jig may be scraped by the spacer 1 and minuteforeign matter may be generated.

The material of the spacer 1 is not specifically limited, and examplesof the material include aluminosilicate glass, soda-lime glass, sodaaluminosilicate glass, alumino-borosilicate glass, borosilicate glass,quartz glass, and crystallized glass. An example of aluminosilicateglass that can be used contains 59 to 63 mass % of silicon dioxide(SiO₂), 5 to 16 mass % of aluminum oxide (Al₂O₃), 2 to 10 mass % oflithium oxide (Li₂O), 2 to 12 mass % of sodium oxide (Na₂O), and 0 to 5mass % of zirconium oxide (ZrO₂). This glass is preferable for thespacer 1 in terms of its high rigidity and low coefficient of thermalexpansion. An example of soda-lime glass that can be used contains 65 to75 mass % of SiO₂, 1 to 6 mass % of Al₂O₃, 2 to 7 mass % of CaO, 5 to 17mass % of Na₂O, and 0 to 5 mass % of ZrO₂. This glass is relatively softand easy to grind and polish, and is therefore suitable for the spacer 1in terms of facilitating an increase in surface smoothness.

The glass spacer 1 is preferably used in combination with a magneticdisk 5 that is obtained by forming a magnetic film on a glass substrate.In this case, the spacer 1 and the magnetic disk 5 have substantiallythe same thermal expansion rate, and even if the internal temperature ofthe HDD apparatus changes, the spacer 1 and the magnetic disk 5 arehardly displaced or rubbed against each other as a result of apositional change occurring between the spacer 1 and the magnetic disk 5due to a difference in the amount of thermal expansion, and thereforethe occurrence of an error in reading a recorded signal, which would becaused by displacement, and generation of minute particles, which wouldbe caused by rubbing, can be suppressed.

A blank for the glass spacer 1 can be obtained using any method, such asa method of manufacturing a glass plate using a float method, a downdraw method, or the like and cutting the glass plate into a ring shape,a method of molding molten glass through pressing, or a method ofmanufacturing a glass tube through tube drawing and slicing the glasstube to a suitable length. The outer circumferential edge surface 2, theinner circumferential edge surface 3, and the main surfaces 4 of thethus formed ring-shaped glass plate are subjected to chamfering or othershape processing, grinding, polishing, etching, or the like, asnecessary. The main surfaces 4 can be ground through, for example,lapping that is performed using loose abrasive particles, or a planetarygear method that is performed using fixed abrasive diamond particles(diamond pads) or the like. The main surfaces 4 can be polished through,for example, a planetary gear method that is performed using a polishingsolution that contains minute particles of cerium oxide or silicondioxide.

If abrasive diamond particles or the like are used as fixed abrasiveparticles in polishing the main surfaces 4, one particle may be used asa fixed abrasive particle, or an aggregate that is formed by bonding aplurality of particles through vitrification or the like may be used asa fixed abrasive particle. In particular, fixed abrasive particles thatcontain diamond cut glass sharply, and are therefore preferable in termsof increasing the average inclination RΔa of the surface shape. Fixedabrasive particles are dispersed and are fixed in resin, for example.

Fixed abrasive particles preferably have an average particle diameter(D50) of 5 to 100 μm. If an aggregate formed by bonding a plurality ofparticles through vitrification or the like is used as one fixedabrasive particle, the average particle diameter (D50) of the particlesis preferably 0.5 to 15 μm, and the average particle diameter (D50) ofaggregates is preferably 5 to 100 μm. The average particle diameter(D50) is a particle diameter at which a cumulative curve reaches 50%when the cumulative curve is determined by setting the total volume ofpowder particles in the particle size distribution measured using alight scattering method to 100%.

The above-described grinding or polishing of the main surfaces 4 can beperformed using a double-side grinding apparatus (or polishingapparatus) that includes upper and lower surface plates and is capableof simultaneously grinding (or polishing) two main surfaces of aworkpiece through a planetary gear movement.

The surface roughness Ra and the average inclination RΔa can be adjustedby, for example, adjusting the size of loose abrasive particles or fixedabrasive particles, the pressure applied by the upper and lower surfaceplates (i.e., a load applied to the workpiece), the manner of changingpressure (for example, changing the pressure in a plurality of stages),the processing time of grinding or polishing, or the like. For example,if the main surfaces are ground using diamond pads, the surfaceroughness Ra and/or the average inclination RΔa can be increased byincreasing the size of fixed abrasive particles. Here, if aggregates areused as fixed abrasive particles, tendencies vary according to the sizeof the particles that are included in the aggregates, in addition to thesize of the aggregates, and accordingly the surface roughness Ra and/orthe average inclination RΔa can be adjusted as appropriate. Further, thesurface roughness Ra and/or the average inclination RΔa can be increasedby increasing the pressure applied by the upper and lower surfaceplates.

After the above-described processing, chemical polishing (etching) mayalso be performed using an etching solution that contains hydrofluoricacid or silicofluoric acid. The surface roughness Ra and/or the averageinclination RΔa can be changed by adjusting components of the etchingsolution, the concentration of the etching solution, the processingtime, or the like. After grinding and/or etching, polishing may befurther performed. The surface roughness Ra and/or the averageinclination RΔa can be reduced through polishing. Etching may beperformed after polishing. The main surfaces 4 that have a desiredsurface shape can be formed by performing the above-described grindingand polishing in combination as appropriate. It is preferable to grindand/or polish the outer circumferential edge surface 2 and the innercircumferential edge surface 3 of the spacer 1, and subsequently grindand/or polish the main surfaces 4.

Although dimensions of the spacer 1 may be changed as appropriateaccording to the specifications of the HDD into which the spacer 1 isinstalled, if the spacer 1 is to be used in an HDD apparatus for anominal size of 3.5 inches, the outer diameter (diameter of the outercircumferential edge surface 2) is 31 to 33 mm, for example, the innerdiameter (diameter of the inner circumferential edge surface 3) is 25mm, for example, and the thickness is 1 to 4 mm, for example. Chamferedsurfaces may be provided by chamfering inner circumferential or outercircumferential edge portions of the main surfaces 4, as appropriate.

Experimental Examples

In order to confirm the effects of the spacer 1, spacers (Samples 1 to30) having different surface irregularities in the main surfaces weremanufactured. The manufactured spacers had an inner diameter of 25 mm,an outer diameter of 32 mm, and a thickness of 2 mm. The spacers hadchamfered surfaces that had an angle of 45° and a width in a radialdirection of 150 μm, and the specifications of the chamfered surfaceswere common between all of the spacers. First, an outer circumferentialedge portion and an inner circumferential edge portion of a ring-shapedglass blank that was cut out from a glass plate were ground using aformed grindstone to form an outer circumferential edge surface, aninner circumferential edge surface, and a chamfered surface. Next, mainsurfaces were ground using a planetary gear-type double-side grindingapparatus in which aggregates formed by bonding minute diamond particlesthrough vitrification were used as fixed abrasive particles in grindingpads that were affixed to upper and lower surface plates. In order toform various surface irregularities in the main surfaces, the size ofthe fixed abrasive particles included in the grinding pads, the loadapplied by the surface plates, the grinding processing time, and thelike were changed. The surface roughness Rz of the outer circumferentialedge surface and the inner circumferential edge surface was fixed to 5μm, and the surface roughness Ra and the average inclination RΔa of themain surfaces 4 were changed. It should be noted that, after theabove-described grinding was performed using the grinding pads includingthe fixed abrasive particles, lapping of the main surfaces using looseabrasive particles, polishing, or etching was appropriately performed incombination as necessary.

Evaluation of Adhesion

As shown in FIG. 3, three magnetic disks (including main surfaces havinga surface roughness Ra of 0.2 nm) and four spacers that weremanufactured as described above were installed in a test apparatus,which was prepared simulating an HDD apparatus, the magnetic disks andthe spacers were pressed against each other using the top clamp 16, and,after the test apparatus was left to stand for 30 minutes, the magneticdisks and the spacers were separately taken out from the apparatus. Themagnetic disks that were used were obtained by forming a magnetic filmor the like on a nominal 3.5-inch glass substrate for a magnetic diskhaving an outer diameter of 95 mm, an inner diameter of 25 mm, and athickness of 0.635 mm, and a lubricant was applied to the outermostsurfaces of the magnetic disks with a thickness of 1 nm. Specifically,whether or not adhesion (separation failure) occurred was confirmedusing a vacuum suction jig including a ring-shaped suction portion thatsucks approximately an entire main surface of a spacer (or sucks aninner circumferential edge-side portion of a main surface when removinga magnetic disk 5).

Evaluation of Attachment of Lubricant

In order to evaluate the possibility of adhesion between the magneticdisks and the spacers, evaluation was performed regarding attachmentmarks of the lubricant formed on the magnetic disks after installationof the magnetic disks and the spacers. The magnetic disks that were usedwere obtained by forming a magnetic film or the like on a nominal3.5-inch glass substrate for a magnetic disk having an outer diameter of95 mm, an inner diameter of 25 mm, and a thickness of 0.635 mm, and thelubricant was applied to the outermost surfaces of the magnetic diskswith a thickness of 1 nm. Unlike the example shown in FIG. 3 in whichthree magnetic disks and four spacers were used, eight magnetic disks(having a surface roughness Ra of 0.2 nm) and nine spacers that weremanufactured as described above were installed in a test apparatus,which was prepared simulating an HDD apparatus, the magnetic disks andthe spacers were pressed against each other using the top clamp, and,after the test apparatus was left to stand for 60 minutes, the magneticdisks and the spacers were separately taken out from the apparatus(i.e., an installation and separation operation was performed). Afterthe above-described operation, the presence or absence of attachmentmarks of the lubricant was checked by visually inspecting portions ofthe main surfaces of the magnetic disks, which were located on the innercircumferential edge surface side and were in contact with the mainsurfaces of the spacers, by irradiating the portions with light emittedfrom a converging lamp in a dark room. The lubricant is a liquid, andtherefore a portion of the lubricant may be attached to recesses in thesurfaces of the spacers due to the influence of a meniscus force.Attachment marks indicate that the thickness of the lubricant is noteven. If the lubricant is attached, when the above-describedinstallation and separation operation is performed two or more times,the possibility of the occurrence of adhesion increases as a result ofthe attached lubricant filling some of the grooves that constitute theuneven shape of the main surfaces of the spacers, and thereforeattachment of the lubricant is not preferable. Attachment of thelubricant was evaluated based on the following standards.

-   Level 1: The number of magnetic disks having attachment marks is one    or less.-   Level 2: The number of magnetic disks having attachment marks is two    or three.-   Level 3: The number of magnetic disks having attachment marks is    four or more.

TABLE 1 Surface Average roughness inclination Presence Evaluation of Ra[μm] RΔa of or absence attachment of spacers spacers of adhesion oflubricant Sample 1  0.3 0.01 Present — Sample 2  0.3 0.02 Absent Level 3Sample 3  0.3 0.04 Absent Level 3 Sample 4  0.3 0.05 Absent Level 2Sample 5  0.3 0.08 Absent Level 2 Sample 6  0.3 0.10 Absent Level 1Sample 7  0.3 0.12 Absent Level 1 Sample 8  0.3 0.16 Absent Level 1Sample 9  0.3 0.20 Absent Level 1 Sample 10 0.3 0.25 Absent Level 1Sample 11 0.5 0.01 Present — Sample 12 0.5 0.02 Absent Level 3 Sample 130.5 0.05 Absent Level 2 Sample 14 0.5 0.10 Absent Level 1 Sample 15 0.50.20 Absent Level 1 Sample 16 0.5 0.25 Absent Level 1 Sample 17 0.1 0.01Present — Sample 18 0.1 0.02 Absent Level 3 Sample 19 0.1 0.05 AbsentLevel 2 Sample 20 0.1 0.10 Absent Level 1 Sample 21 0.1 0.20 AbsentLevel 1 Sample 22 0.7 0.01 Present — Sample 23 0.7 0.02 Absent Level 3Sample 24 0.7 0.05 Absent Level 2 Sample 25 0.7 0.10 Absent Level 1Sample 26 0.7 0.20 Absent Level 1 Sample 27 0.7 0.25 Absent Level 1Sample 28 1.0 0.10 Absent Level 1 Sample 29 1.0 0.20 Absent Level 1Sample 30 1.0 0.30 Absent Level 1

Samples 1 to 30 in the above Table 1 show that, if the surface roughnessRa of the main surfaces is not larger than 1.0 μm and the averageinclination RΔa of the main surfaces is at least 0.02, an adhesive forceis reduced and adhesion is suppressed.

Further, the evaluation results regarding attachment of the lubricantshow that, if the average inclination RΔa is at least 0.05, attachmentof the lubricant is suppressed, and if the average inclination RΔa is atleast 0.10, attachment of the lubricant is further suppressed.Therefore, if the average inclination RΔa is at least 0.05, or at least0.10, adhesion is unlikely to occur even if the operation for installingand separating the magnetic disks and the spacers is performed two ormore times.

It should be noted that a metal film with a constant thickness of 1 μm,specifically, a metal film made of a Ni—P alloy (P: 10 mass %, Ni: theremaining portion) was formed on the outer circumferential edge surface2, the inner circumferential edge surface 3, and the main surfaces 4 ofthe spacers 1 of Sample 7 through electroless plating. The spacers 1provided with the metal film were installed in the HDD apparatus 10shown in FIG. 3. At this time, electrical conduction between the spindle14 and all of the magnetic disks 5 and the spacers 1 was confirmed usinga tester. That is, it can be said that, as a result of the metal filmbeing formed on the spacers 1, static electricity is unlikely toaccumulate in the magnetic disks 5 and the spacers 1 and an effect ofsuppressing adsorption of foreign matter and minute particles to themagnetic disks 5 and the spacers 1 can be achieved, for example.

The above clearly shows the effects of the present embodiment.

The above-described spacers 1 can be manufactured as follows. That is,one embodiment of the present invention is a method for manufacturing aring-shaped spacer 1 to be arranged in contact with a magnetic disk 5 ina hard disk drive apparatus.

This manufacturing method includes grinding main surfaces of aring-shaped glass blank, which is a blank for the spacer 1, using aplanetary gear-type double-side grinding apparatus in which fixedabrasive particles that include minute diamond particles are included ingrinding pads that are affixed to upper and lower surface plates.

According to one embodiment, it is preferable that fixed abrasiveparticles include aggregates that are formed by bonding minute diamondparticles through vitrification.

Through grinding performed in this manufacturing method, it is possibleto make the main surfaces of the spacer that come into contact withmagnetic disks have a surface roughness Ra of not larger than 1.0 μm andan average inclination RΔa of at least 0.02.

Although the glass spacer and the hard disk drive apparatus of thepresent invention have been described in detail, the present inventionis not limited to the above-described embodiment, working examples, andthe like, and it goes without saying that various modifications andchanges can be made within a scope not departing from the gist of thepresent invention.

What is claimed is:
 1. A method for manufacturing the ring-shaped glassspacer to be arranged in contact with a magnetic disk in a hard diskdrive apparatus, the method comprising: preparing a ring-shaped glassblank; and grinding main surfaces of the ring-shaped glass blank byusing grinding pads that include diamond particles as fixed abrasiveparticles.
 2. The method according to claim 1, wherein the grinding ofthe main surfaces of the ring-shaped glass blank is performed by usinggrinding pads each including, as each of the fixed abrasive particles,an aggregate formed by bonding the diamond particles throughvitrification.
 3. The method according to claim 1, further comprisingperforming shape processing on the ring-shaped glass blank to provide atransitional surface between at least one of the main surfaces of thering-shaped glass blank and one of an outer circumferential edge surfaceand an inner circumferential edge surface.
 4. The method according toclaim 3, wherein the transitional surface is a chamfered surface.
 5. Themethod according to claim 2, further comprising performing shapeprocessing on the ring-shaped glass blank to provide a transitionalsurface between at least one of the main surfaces of the ring-shapedglass blank and one of an outer circumferential edge surface and aninner circumferential edge surface.
 6. The method according to claim 5,wherein the transitional surface is a chamfered surface.
 7. The methodaccording to claim 1, wherein the grinding is performed such that asurface roughness Ra of the main surfaces of the ring-shaped glass blankis not larger than 1.0 μm, and an average inclination RΔa of the mainsurfaces that is obtained using the following Equation (1) is at least0.02, $\begin{matrix}{{R\Delta a} = {\frac{1}{n}{\sum\limits_{i = 1}^{n}{\frac{dz_{i}}{dX}}}}} & (1)\end{matrix}$ here, dz_(i)/dX is expressed by the following Equation(2), ΔX represents a data interval (μm) between measurement data piecesof surface roughness, z_(i) (i is a natural number) represents the i-thmeasurement data piece, and n represents a total number (n>6) ofmeasurement data pieces $\begin{matrix}{{\frac{dz_{i}}{dX} = {\frac{1}{{60 \cdot \Delta}\; X}( {z_{i + 3} - {9z_{i + 2}} + {45z_{i + 1}} - {45z_{i - 1}} + {9z_{i - 2}} - z_{i - 3}} )}}.} & (2)\end{matrix}$
 8. The method according to claim 2, wherein the grindingis performed such that a surface roughness Ra of the main surfaces ofthe ring-shaped glass blank is not larger than 1.0 μm, and an averageinclination RΔa of the main surfaces that is obtained using thefollowing Equation (1) is at least 0.02, $\begin{matrix}{{R\Delta a} = {\frac{1}{n}{\sum\limits_{i = 1}^{n}{\frac{dz_{i}}{dX}}}}} & (1)\end{matrix}$ here, dz_(i)/dX is expressed by the following Equation(2), ΔX represents a data interval (μm) between measurement data piecesof surface roughness, z_(i) (i is a natural number) represents the i-thmeasurement data piece, and n represents a total number (n>6) ofmeasurement data pieces $\begin{matrix}{{\frac{dz_{i}}{dX} = {\frac{1}{{60 \cdot \Delta}\; X}( {z_{i + 3} - {9z_{i + 2}} + {45z_{i + 1}} - {45z_{i - 1}} + {9z_{i - 2}} - z_{i - 3}} )}}.} & (2)\end{matrix}$
 9. The method according to claim 3, wherein the grindingis performed such that a surface roughness Ra of the main surfaces ofthe ring-shaped glass blank is not larger than 1.0 μm, and an averageinclination RΔa of the main surfaces that is obtained using thefollowing Equation (1) is at least 0.02, $\begin{matrix}{{R\Delta a} = {\frac{1}{n}{\sum\limits_{i = 1}^{n}{\frac{dz_{i}}{dX}}}}} & (1)\end{matrix}$ here, dz_(i)/dX is expressed by the following Equation(2), ΔX represents a data interval (μm) between measurement data piecesof surface roughness, z_(i) (i is a natural number) represents the i-thmeasurement data piece, and n represents a total number (n>6) ofmeasurement data pieces $\begin{matrix}{{\frac{dz_{i}}{dX} = {\frac{1}{{60 \cdot \Delta}\; X}( {z_{i + 3} - {9z_{i + 2}} + {45z_{i + 1}} - {45z_{i - 1}} + {9z_{i - 2}} - z_{i - 3}} )}}.} & (2)\end{matrix}$
 10. The method according to claim 5, wherein the grindingis performed such that a surface roughness Ra of the main surfaces ofthe ring-shaped glass blank is not larger than 1.0 μm, and an averageinclination RΔa of the main surfaces that is obtained using thefollowing Equation (1) is at least 0.02, $\begin{matrix}{{R\Delta a} = {\frac{1}{n}{\sum\limits_{i = 1}^{n}{\frac{dz_{i}}{dX}}}}} & (1)\end{matrix}$ here, dz_(i)/dX is expressed by the following Equation(2), ΔX represents a data interval (μm) between measurement data piecesof surface roughness, z_(i) (i is a natural number) represents the i-thmeasurement data piece, and n represents a total number (n>6) ofmeasurement data pieces $\begin{matrix}{{\frac{dz_{i}}{dX} = {\frac{1}{{60 \cdot \Delta}\; X}( {z_{i + 3} - {9z_{i + 2}} + {45z_{i + 1}} - {45z_{i - 1}} + {9z_{i - 2}} - z_{i - 3}} )}}.} & (2)\end{matrix}$
 11. The method according to claim 1, further comprisingforming a conductive film on at least one of the main surfaces of theglass spacer.
 12. The method according to claim 2, further comprisingforming a conductive film on at least one of the main surfaces of theglass spacer.
 13. The method according to claim 3, further comprisingforming a conductive film on at least one of the main surfaces of theglass spacer.
 14. The method according to claim 5, further comprisingforming a conductive film on at least one of the main surfaces of theglass spacer.
 15. The method according to claim 7, further comprisingforming a conductive film on at least one of the main surfaces of theglass spacer.
 16. The method according to claim 8, further comprisingforming a conductive film on at least one of the main surfaces of theglass spacer.
 17. The method according to claim 9, further comprisingforming a conductive film on at least one of the main surfaces of theglass spacer.
 18. The method according to claim 10, further comprisingforming a conductive film on at least one of the main surfaces of theglass spacer.